Datacenter Activation Coordination (DAC) Mode is a property of an Exchange DAG that is used to prevent 'split-brain' syndrome where multiple members activate their databases without knowing whether or not the other members have their databases mounted. What happens when DAC mode is enabled and set to 'dag only': After a failure of Exchange, Exchange will use the DACP protocol to determine the current state of a DAG and whether the databases should be mounted on a server.  DAC mode requires Read more [...]

According to Microsoft, Exchange DAG replication latency should be below 500ms roundtrip. This DAG latency requirement has limited my deployment options in the past to very specific WAN scenarios like MPLS, Point to Point Wifi, etc.  Many customers wishing to deploy a DAG across a VPN didn’t meet the latency requirements.  In other words, I haven't implemented an Exchange DAG that is replicating across the internet. From Microsoft: "Regardless of their geographic location relative to other Read more [...]